Hydrometallurgical treatment of metal-bearing materials, such as metal ores, metal-bearing concentrates, and other metal-bearing substances, has been well established for many years. Moreover, leaching of metal-bearing materials is a fundamental process utilized to extract metals from metal-bearing materials. In general, the first step in this process is contacting the metal-bearing material with an aqueous solution containing a leaching agent or agents which extract the metal or metals from the metal-bearing material into solution to yield an aqueous metal-bearing pregnant leach solution. For example, in copper leaching operations, especially operations involving copper recovery from copper-containing minerals such as chalcopyrite, chalcocite, covellite, malachite, pseudomalachite, azurite, chrysocolla, and cuprite, sulfuric acid in an aqueous solution is contacted with copper-bearing ore. During the leaching process, acid in the leach solution may be consumed and various soluble metal components are dissolved, thereby increasing the metal content of the aqueous solution.
The aqueous leach solution containing the leached metal can then be treated via a process referred to as solution extraction (also referred to as solvent or liquid-liquid extraction or liquid ion exchange) wherein the aqueous leach solution is contacted with an organic solution comprising a metal extraction reagent, for example, an aldoxime and/or ketoxime or a mixture thereof. The metal extraction reagent extracts the metal from the aqueous phase into the organic phase. Moreover, during the solution extraction process for copper and certain other metals, leaching agent may be regenerated in the aqueous phase. For example, in the case where sulfuric acid is the leaching agent, sulfuric acid is regenerated in the aqueous phase when copper is extracted into the organic phase by the extraction reagent.
In a typical agitation leaching process for copper, followed by solution extraction, the leach solution may be diluted to a lesser or greater extent with acidified water in conjunction with the solid-liquid separation process needed to provide a clarified leach liquor and solid discharge. The diluted clarified leach solution then typically undergoes solution extraction at a solution-extraction plant or facility, wherein a primary metal value, for example, copper, is removed from, and the sulfuric acid concentration is increased in, the aqueous phase. A portion of this copper-depleted, acid-containing aqueous phase, now called the raffinate, may be recycled back to the leaching process, recycled to the front of the solid-liquid separation process, and/or forwarded to secondary metal extraction processes, including but not limited to cobalt recovery. Alternatively, leach streams of different grades may be treated at separate plants or facilities and the respective raffinates and organic solutions may be cycled or recycled within such plants or facilities.
Using typical leaching and solution extraction processes, large concentrations of soluble metal and metal precipitate of a primary metal value can be lost in the metal-depleted, acid-containing raffinate. These losses lead to inefficiencies and low overall process yields. Furthermore, these high metal concentrations in the raffinate may make recovery of secondary metals relatively costly and possibly impractical.
Typically, a solution-extraction plant includes a single circuit to extract the metal values from the leach solution. Although this can work relatively well in some circumstances, recovery of a primary metal value from leach solutions using a single-circuit solution-extraction plant or facility can lead to significant down-time and decreased metal output of the primary metal value when the solution extraction circuit is inoperative due to, for example, necessary repairs or maintenance.
Accordingly, a process and system that use solution extraction to extract a primary metal value from a leach solution and decrease the concentration of the primary metal value, for example, copper, in the resultant raffinate solution, while simultaneously providing for increased loading of the primary metal value in the metal extraction reagent, are desirable. In addition, an improved process and system that reduce plant down-time are desired.